The invention relates to a driver assistance system in a motor vehicle for determining an acceleration strategy and for automatically implementing the acceleration strategy.
In principle, many driver assistance systems configured as a speed control system are already known that regulate the speed of the motor vehicle to a prescribed desired or setpoint speed. Besides these longitudinal control systems, it is today already possible to purchase even longitudinal control systems extended by distance control, what are known as distance-based longitudinal control systems or speed control systems, from some manufacturers. Systems of this kind that are provided—for example by the applicant of the present patent application under the name “Active Cruise Control”—allow the motor vehicle to be driven automatically at a desired or correspondingly lower speed while maintaining a desired distance from a vehicle travelling in front. When a distance sensor system fitted to the motor vehicle, which distance sensor system can operate particularly on a radar basis, detects a target object or (motor) vehicle travelling in front in its own lane, its own speed is matched—for example by prompting a suitable braking torque—to the speed of the motor vehicle travelling in front or the target object. This is done such that distance control in the “active speed-of-travel control” or the relevant longitudinal control system automatically regulates and maintains a situation-appropriate distance from the motor vehicle or target object travelling ahead. Termination of the subsequent travel is followed by acceleration to the prescribed desired speed again.
Further, what are known as speed limiting systems are known that prevent the speed selected by the driver from being exceeded.
DE 10 2012 211 967 A1 describes a combination of a speed limiting system and a speed control system, wherein the maximum speed of the speed limiting system instead of the selected set speed is adoptable as a (new) setpoint speed for the speed control.
Finally, in more recent vehicles, there are also driver assistance systems that can predictively identify a speed restriction, either from map data of a navigation system and/or by means of image processing, and continuously display it to the driver, so that the driver can independently match his speed to the speed restriction as required (e.g. BMW Speed Limit Info).
DE 10 2008 018 421 A1 discloses a driver assistance system for sending and receiving speed data and/or traffic density data for controlling a speed control system, which driver assistance system takes the received data as a basis for determining an admissible maximum speed and communicates the latter to the driver by outputting an appropriate notification. The driver can adopt this stipulation of the admissible speed for his speed control system by means of simple operation. Similarly, when the speed limit is left, this is displayed to the driver.
It is thus an object of the invention to provide a driver assistance system that, on termination of a speed limit, determines and if need be implements an acceleration strategy that is agreeable and comprehensible to the driver.
This and other objects are achieved by a driver assistance system in accordance with embodiments of the invention.
The driver assistance system according to the invention essentially comprises three core elements:                a detection system for identifying events ahead that, on account of a currently valid speed limit being lifted, allow the current speed to be increased (to a new higher target speed),        a notification system for outputting a request notification to the driver for allowing the acceleration strategy to be automatically implemented, and        a functional unit for determining an acceleration strategy for increasing the speed.        
Only when the driver allows the automatic implementation of the acceleration strategy by appropriately acknowledging the request notification does the functional unit prompt the automatic implementation of the acceleration strategy by transmitting appropriate control signals to the drive and/or braking unit.
The relevant events ahead that allow the current speed to be increased can be identified either from map data of a navigation system and/or by use of image processing by a predictive sensor system and/or by way of a Car-to-X communication unit by virtue of reception of relevant data from other vehicles or from road signs or traffic control systems. The events ahead may therefore be, by way of example, the lifting of temporary or permanent speed restrictions that are either indicated directly on a road sign or can be derived from the general traffic rules on the basis thereof (e.g. a speed restriction of 50 km/h applies in Germany for travelling through a town). The target speed definitive for the acceleration strategy based on the location of the event ahead may be either the (higher) maximum permitted speed following the sign lifting the restriction (the “derestriction sign”) or a speed that differs upward or downward by a prescribed magnitude, the magnitude and the direction of the difference possibly being selectable by the driver in a central vehicle menu, for example. Similarly, the speed to be reached may also be a desired or setpoint speed prescribed by the driver, particularly when the desired or setpoint speed prescribed by the driver is lower than a maximum speed permitted after the event that lifts the current speed limit.
In the case of the invention, it is assumed that the vehicle initially either moves at an appropriate restricted initial speed on account of an active speed limiter (e.g. Speed Limit Device) that takes into consideration the speed limit or at the appropriate initial speed on account of an active, generally known speed controller (e.g. ACC).
The invention is further based on the principle that when a future termination of a speed limit is identified in advance, an offer of automatic speed increase can fundamentally be made only in a very restricted manner, since it is always necessary to ensure that within the range of the (still existing) speed limit it is not possible (or only very slightly possible) to exceed the admissible maximum speed on the basis of the traffic rules. Further, however, it is also known that a normal driver accelerates his vehicle slightly before actually reaching the derestriction sign and, after the derestriction sign, wants to quickly reach the new admissible maximum speed or his desired speed by means of appropriate pedal operation.
Taking the above insight into consideration, the invention provides that the request notification is outputable to the driver at a defined time before the event ahead that lifts the current speed limit is actually reached, and the functional unit, on acknowledgement of the request notification, prompts an acceleration strategy, which is set up as a two-stage acceleration strategy, before the event ahead that lifts the current speed limit is reached. Before actually reaching the event that lifts the speed limit, the functional unit determines an appropriate acceleration strategy that, when automatic implementation before the relevant event is desired by the driver, firstly shows an acceleration behavior that is comprehensible to the driver, but at the same time also takes account of the existing traffic rules in a comprehensible manner. To this end, the invention initially involves determining, as an acceleration strategy, a two-stage acceleration strategy that is implemented at least in a matched form if the driver acknowledges the request notification before the event ahead that lifts the current speed limit is reached. Advantageously, this involves a smaller acceleration being prompted in the first stage of the two-stage acceleration strategy than in the second stage of the two-stage acceleration strategy.
Further, the acceleration strategy is advantageously set up such that the first stage of the two-stage acceleration strategy is implemented up to the location of the event ahead at which the currently valid speed limit is lifted and the second stage of the two-stage acceleration strategy is implemented only from when the event ahead at which the currently valid speed limit is lifted is reached. In other words, at the location of the event ahead at which the currently valid speed limit is lifted, there is therefore a changeover from the first acceleration program (=first stage of the two-stage acceleration strategy) to a second acceleration program (=second stage of the two-stage acceleration strategy). The first acceleration program contains mapping showing that the offer to increase speed is made only an applicable distance before the derestriction sign. If the driver then allows automatic implementation of the acceleration strategy by means of appropriate control element operation, the acceleration is selected exactly such that at the location of the derestriction sign the speed limit ending at that location is exceeded only by a small—possibly selectable—magnitude. The second acceleration program is, by contrast, selected after the derestriction sign such that the acceleration to the new target speed is firstly effected comfortably, but at the same time the speed difference is also regulated as quickly as possible. With an appropriately chosen acceleration in the two acceleration programs, it is therefore possible to ensure that the driver already experiences slight acceleration of the vehicle up to the derestriction sign, and acceleration of the vehicle to the new, higher target speed is performed only from the derestriction sign onward.
Advantageously, the defined time at which the request notification is output is determined and accordingly output on the basis of prescribed parameters, particularly on the basis of the distance from the location of the event ahead and/or on the basis of the speed difference from the current speed, or the maximum speed allowed on the basis of the speed limit, and a target speed permitted or desired after the speed limit has been lifted. In particular, the defined time at which the request notification is output can be prescribed such that the request notification is output at a prescribed distance from the location of the event ahead, so that on acknowledgement by the driver it is possible for automatic implementation of the acceleration strategy to be effected.
As already mentioned above, in a further advantageous refinement of the invention, in the first stage of the two-stage acceleration strategy, an acceleration is prompted such that the speed limit lifted at the location of the event ahead is exceeded only by a prescribed, advantageously adjustable, small speed magnitude at said location. The possibly selectable speed offset can be chosen, by way of example, by means of a central operator control element using an appropriate choice of offset, so that it can be used for all further acceleration strategies. If desired, it is also possible to select that at the location of the event ahead, the speed limit lifted at that location is not yet exceeded.
In contrast to the acceleration in the first stage, in the second stage of the two-stage acceleration strategy, an acceleration can be prompted such that a target speed permitted or desired after the speed limit has been lifted is reached within the shortest possible time or within a prescribed time window, a prescribed maximum acceleration advantageously not being able to be exceeded. Advantageously, in the second stage of the two-stage acceleration strategy, the acceleration can in this case be prescribed on the basis of the speed difference from the current speed and a target speed permitted or desired after the speed limit has been lifted and/or on the basis of a current mode of operation of the vehicle (e.g. sports mode, comfort mode or ECO mode).
Advantageously, as part of the two-stage acceleration strategy, stipulation of the acceleration can also take into consideration possible action in the transmission control, so that prescribed or desired transmission control is maintained. As such, in the first stage of the two-stage acceleration strategy, an acceleration can be requested such that a downshift in the transmission of the vehicle is avoided or such action is taken in the transmission control of the vehicle as to prevent a downshift request, possibly present on account of the acceleration requirement. By contrast, in the second stage of the two-stage acceleration strategy, such an acceleration can be requested as to request and implement a downshift in the transmission, i.e. an acceleration that requires a downshift in the transmission is deliberately requested. Hence, the first acceleration is provided gently and a corresponding dynamic impression is supported by the downshift only at the location of the event ahead (on transition to the second acceleration stage).
In principle, determination of the acceleration strategy can take into consideration not only the critical constraints, such as e.g. speed difference between the current speed and the target speed, distance from the location of critical events ahead and/or desired target speed, but also further criteria that have an influence on the acceleration action of the vehicle. The influencing factors may particularly be current influencing factors, but it is also possible to take into consideration already known influencing factors, influencing factors occurring in the future and influencing factors influencing acceleration that will occur up to the location of the event ahead or in the subsequent acceleration phase. By way of example, they may be road inclination, wind conditions and other weather conditions, the current loading of the vehicle, or the like.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.